Safety. Environmental footprint. Cost efficiency. In the oil and gas industry’s ever-expanding lexicon, no terms have become as top of mind as these critical watchwords that factor into every decision on every well. And nowhere is this more evident than the ongoing challenge of solids control and cuttings disposal.

Solids have been a necessary byproduct of wells from time immemorial. In a world of declining resources and heightened concern about the environment, this is an arena where the industry continues to innovate with systems and methods that are safer and cleaner, and better designed to handle the challenges of underbalanced drilling and longer, deeper and more complicated wells that produce a higher volume of drill cuttings.

New technologies, combined with existing methods that have been tweaked for better performance, are driving the push to continually raise the bar and reduce the environmental footprint in solids control.

“We are seeing much more of a collaborative effort among operators, drilling contractors and service companies to establish better processes and operations in handling solids,” said Don Chamberlain, technical services manager, Newpark Drilling Fluids. “The focus is to take what we’ve been doing and hone it down to where it is efficient and optimize it as much as we possibly can. Safety is our number one priority.”

A shale shaker separates the mud from the cuttings. The mud goes back into the mud pits, located under the grate floor beneath the mud cleaning equipment. The cuttings are dropped into the cuttings box, and the backhoe scoops the cuttings off the bottom of that box. Source: Newpark Drilling Fluids, Dale Shank and Bill Mason Jr

Time-tested tools such as shale shakers, high-speed screening devices, high- and low-speed centrifuges, de-sanders and mud cleaners are still used to separate and remove cuttings from the drilling fluid.

“But we are using better polymers for coagulants, better screen designs and new ways of utilizing the solids control equipment so we get a more efficient cut and removal of solids,” Mr Chamberlain noted. “And, of course, the centrifuges are becoming larger to handle more fluid and more efficient to produce a finer cut.

“What we do with the equipment and how we handle and operate it is based a lot on whether the drilling fluid is oil-based or water-based,” he continued. “Both use similar equipment.”

When the drilling fluid is oil-based, the process typically involves the use of a drying shaker. The drill solids are processed across the drying shaker, which removes much of the oil-based fluid, returning it to the mud system. The cuttings are then placed in a holding tank for disposal.

“The drilling fluid is then further processed, using low-speed and high-speed centrifuges to recover Barite and to further remove drill solids. These drill solids are also placed in the holding tank for disposal,” Mr Chamberlain explained.

For land operations, the process is usually a closed-loop, or zero-discharge, system where the dry cuttings are held until they are transported to an offsite disposal facility or injection site, or they are solidified, based on the regulations of the area.

In a water-based mud operation, the use of a closed-loop system may be required. In this situation, the drilling fluid and cuttings are processed with a coagulating agent and a high-speed centrifuge to improve the separation of the solids. The remaining water is put back into the mud system. Depending on regulations, the cuttings are left on location or transported to a disposal facility.

Pad drilling also has improved efficiency in handling and disposing of solids. “With pad drilling, we have one road and one solids control catch tank for one area, serving anywhere from four to 30 wells,” Mr Chamberlain said. “So we have less transportation and lower emissions, and we use less fuel and have fewer accidents.”

Determining which, and how much, equipment to utilize is examined on a case-by-case basis and is greatly determined by environmental regulations that govern the location of the operation and dictate how the cuttings are to be disposed of.

“Oil-based cuttings may involve more drying equipment,” said Dennis Welch, performance services manager, Newpark. “That can be cost-effective at the beginning phase of a well, when we’re drilling bigger holes and we have more cuttings,” he noted. “But when we get down to production holes on wells, where we are generating a lot less waste, we have to weigh the costs and the benefits. We don’t want equipment that is sitting idle, not paying for itself. When possible, we set up an open-top catch tank with a backhoe and try and recycle the liquids back into the circulating system and put the cuttings in dump trucks for disposal.”

“The higher the cost of trucking and disposal, the more attractive the equipment becomes. If there is a disposal site fairly close that charges a reasonable price, then we can reduce the amount of processing equipment on site,” Mr Welch said.

Because inland water is all zero-discharge regardless of the mud type, the cuttings are dumped to barges. “We try and have good solids control equipment, shakers and recycle pumps,” Mr Welch said. “We try to reclaim the usable fluids back out of the barges, and then everything is tugged to a collection facility.” The waste is taken from the barges to trucks, which haul it to a subsurface injection site.

But the industry is also looking at new techniques that are cleaner and more streamlined to deal with larger holes and faster drilling, which produces more solids and mud.

“On the rig, the trend is toward larger equipment, such as centrifuges, that can handle greater flow rates and remove more solids, especially the smaller solids, from the mud and keep it cleaner,” said Dale Pierce, global product line manager, National Oilwell Varco.

The Multi-Sizer, a triple-deck shale shaker, can handle much higher flow volumes in a smaller area and can capture more solids and handle more mud in a smaller footprint. A video demonstrating this shale shaker is available below.

“We now have a triple-deck shale shaker, called a Multi-Sizer, that is capable of handling much higher flow volumes in a smaller area. It allows us to capture more solids and handle more mud in a smaller footprint. For example, instead of having six or eight shale shakers, we have three or four of this new design that can do the same job.”

With the increase in underbalanced drilling and long, horizontal wells and tight gas formations needing greater stabilization, operators also are looking at what Mr Pierce called “designer solids,” in conjunction with a stress cage, to stabilize the wellbore. “We actually put a particular size of solids into the mud to plate out to the many fractures along the sides of the wellbore,” he explained.

“In this case, we don’t want the shale shakers to remove those solids, we want to save them, which ultimately reduces the cost,” he continued. “The triple-deck shaker is capable of selectively removing those solids, something we have not been able to do in the past. We remove these designer solids and then put them back into the mud. We put the mud over a very fine shaker screen and remove as much of the low-gravity solids as we can.” The mud is then put through a centrifuge, where it is cleaned.

The process of selectively removing solids is increasingly being used for underbalanced drilling, Mr Pierce continued. “We de-weight the mud with a solid that is less dense than water but provides some viscosity. But we don’t want that removed either. It’s a matter of putting something into the mud that we want to keep in the mud, and then removing it with a shale shaker in such a way that we can capture it and put it back into the mud.”

The industry also has developed a new cuttings disposal technique for zero-discharge offshore areas. The mechanism uses positive pressure pneumatics that blow the cuttings into a storage area and then onto a boat, which then transports the cuttings to an onshore disposal facility. The system is used in place of the skip and ship method, where cuttings are placed in a cuttings box on the rig and moved by a crane until they are loaded onto a boat for transport.

“The new system saves time and is much safer because it eliminates handling steps and the use of the crane, which is one of the biggest causes of accidents in the industry,” Mr Pierce said.

At the same time, there is a push to develop ways of treating cuttings on the rig, to achieve an oil retention rate that will allow the cuttings to be discharged rather than transported, which is costly. A device called a hammer mill removes oil using heat generated by friction, Mr Pierce said. Current use of the hammer mill is limited because it takes up space on the rig and has a capacity of only four to five tons per hour.

“So, if a rig is drilling very fast, the cuttings have to be stored in some type of storage mechanism,” he added. “But some of the newer rigs are being designed with an area to accommodate onboard treatment equipment.”

As all segments of the oil and gas industry seek ways to reduce their environmental footprint, new technologies are emerging to foster what has become a familiar mantra: Reclaim. Recycle. Reuse.

Environmental Drilling Solutions (EDS), with operational headquarters in Lafayette, La., has developed a mobile processing system for separating oil-based mud from drill cuttings. The process allows for the reuse of expensive drilling fluids and significantly reduces the need to haul and dispose of oil-based mud wastes. EDS president Chad Hollier says the company’s mobile drying services are proving successful in the shale plays, enhancing the economics for operators to manage their disposal of drill cuttings.

The company has patents pending on its mobile processing equipment, which is being deployed in the Haynesville, Marcellus, Woodford and Eagle Ford shale plays.

“Our original objective was to supply oil-based mud-handling equipment,” Mr Hollier said. But the focus shifted to drill cuttings processing to meet operators’ needs of managing high volumes of drilling wastes, which were putting increased pressure on trucking and the land disposal facilities, he explained. EDS fitted the dryer equipment onto trucks, making the process mobile, thus allowing multiple rigs to be serviced with one system.

The process involves a cuttings dryer using a high G force to remove oil and liquids from the drill cuttings, reducing haul-off volumes by 50%.

“EDS took what we considered to be the best technology available and modified the process to make it work more efficiently and cost-effectively,” Mr Hollier said. The company also utilizes a hydraulic vacuum system that removes the solids and liquids that make up the waste stream from the drill cuttings box and transfers them to the rotating dryer for processing.

The oil-based mud is returned to the rig for reuse, and the drill cuttings, with an oil content of less than 3%, are either buried on location with regulatory approval or trucked to a designated disposal site. The average distance from a well to a disposal site is 200 miles one way.

“Our purpose-built mobile equipment reduces waste volumes and transportation, and recycles the mud that otherwise would be lost on the drill cuttings, adding to disposal costs,” Mr Hollier noted.

At the Baker Hughes waste management facility in Scotland, the “cleaned” solid materials are processed, then used in place of quarried aggregates to cap local landfill sites.

Operators in the North Sea now have access to Baker Hughes’ new centralized waste management facility that processes drill cuttings down to an oil retention rate of less than .5%.

Located north of Aberdeen in Peterhead, Scotland, the Eco-Centre waste management facility can process more than 33,000 tons of drill cuttings and nearly 4 million gallons of liquid waste annually. Several major energy companies are using the facility, which opened in June this year. It features a remote monitoring system where operators can track the processing of their waste online and receive an accounting of their waste management.

The facility was developed by Baker Hughes in conjunction with the Aberdeenshire Council, the Scottish Environmental Protection Agency, Scottish Water and local engineering consultants. “The North Sea is a very established, mature area in terms of technical expertise and environmental awareness and serves as center for training and global research and development,” said Heather Thomas, director, fluids environmental services products for Baker Hughes.

“The Eco-Centre facility is all about planning and having a system in place that allows the industry to be responsible from the outset.”

In using the center, operators transport their waste via truck or boat to the Eco-Centre facility, which is proximate to the Peterhead port. In the past, operators disposed of drill cuttings and liquids at several sites that handled different types of waste. “Transportation to these various facilities could be arduous and require several trips,” Ms Thomas said.

Recovered oil from drill cuttings is reused to fuel the processing mill at Baker Hughes’ Eco-Centre.

The concept behind the facility is to reduce, reclaim, recycle and reuse as much of the waste as possible, she noted. For example, the processed drill cuttings are used in place of quarried aggregates to cap approved local landfill sites. Liquids are treated to remove all solids and hydrocarbons. The recovered oil fuels the processing mill at the center, while reclaimed water is used to cool and rehydrate the recovered solids.

“This is a licensed facility,” she continued. “The licensing regulations for emissions to the atmosphere for discharge of a clean product are very high in this country. And because this area is so heavily licensed and guarded and the regulations are becoming more stringent, new technologies are going to have to come to the forefront.”

The FES Global Research and Development Center, also located at the new facility, is a Baker Hughes R&D hub designed to develop new drilling waste treatment technologies aimed at reducing the environmental impact of the oil and gas industry.

“The world is changing and becoming a lot smaller in terms of education and environmental awareness,” Ms Thomas said. “We have to be 100 percent transparent. And in order to do that, we have to have clear core competencies that maintain the same standards regardless of where in the world we are operating.”

A boat using “slider tanks” transports cuttings to shore for further treatment and disposal in the North Sea. The cuttings were blown from a rig without the use of a crane. A transfer line floats in the water.

Navigating the complicated and sometimes overlapping patchwork of environmental regulations can be a daunting endeavor in the handling and disposal of drill cuttings, which is one of the biggest sources of waste in the oil and gas industry, according to Dale Pierce, global product line manager, National Oilwell Varco.

Old methods such as land farming, the dispersal of waste on leased or private land, is a thing of the past for an industry that must now comply with a growing number of mandates, but that has also made environmental stewardship a priority.

Today, there are strict regulations for the disposal of water-based and oil-based drill cuttings. The multitude of rules varies from sea to sea, country to country and, in the United States, from state to state. In some areas, federal regulations, overseen by the Environmental Protection Agency (EPA) and the Bureau of Land Management (BLM), frequently converge with state regulatory agencies, from the Texas Railroad Commission to the Department of Environmental Protection in Pennsylvania.

“The increasing number of environmental regulations has certainly made solids control and cuttings disposal more challenging,” said Densil Crosby, international operations manager for QTEC, an Aberdeen-based company that audits equipment for operators to ensure their systems are performing at maximum efficiency and meeting regulatory requirements. “We try to keep our clients operating within the environmental regulations of whatever region they are working in,” Mr Crosby said.

Among the more common terms associated with cuttings disposal is zero-discharge, or closed-loop, meaning the cuttings must be removed from the well site and transported to a disposal facility rather than placed in a reserve tank or buried on site. With few exceptions, oil-based cuttings are typically subject to zero-discharge rules.

Rules for disposal of water-based cuttings vary with location. “On land, depending on what jurisdiction we’re in, we’ve got state regulations, BLM regulations and the EPA,” said Don Chamberlain, technical services manager, Newpark Drilling Fluids, who is involved in operations in Colorado, Wyoming, Utah and South Dakota. “We typically choose the most stringent regulations and closely monitor what goes into our mud system to ensure that we are in compliance.”

Water-based mud satisfies a lot of the regulations, but there is a downside if the location is zero-discharge. “Diesel-based mud will generate less waste,” explained Dennis Welch, performance services manager for Newpark. “Because of solids hydration, water-based muds are diluted to reduce the solids, and the mud builds more volume, which you have to dispose of,” he said. “Also, the cuttings are wetter and sloppier.

“In a nutshell, if it’s land and the regulations are zero-discharge, we can’t use a reserve pit,” Mr Welch continued. “We have a ring levee around the rig. Everything must be contained in tanks and put on trucks and hauled offsite. The water-based mud is cheaper per barrel to dispose of, but there is more volume, and we still have to transport it.

“Inland water is always zero-discharge because we are in bays and we can’t dump anything,” Mr Welch added.

Environmental regulations also vary offshore. However, in the case of oil-based cuttings, all offshore areas mandate that the oil be synthetic. “Some areas require that we employ a reinjection technique, where we drill a side well and pump the cuttings back down into the hole,” QTEC’s Mr Crosby said. “In other areas that allow discharging overboard, there are limits on how much we actually discharge.”

Generally speaking, there are two sets of offshore rules throughout the world – North Sea and Gulf of Mexico, said NOV’s Mr Pierce. “In the GOM, which is governed by the EPA, water-based cuttings may be discharged overboard in deepwater.” In the case of synthetic oil-based cuttings, those that retain 6.9% or more of the oil must be transported back to shore for disposal. GOM rules also apply to Brazil and West Africa.

“North Sea rules state that we can’t dispose overboard any cuttings that retain 1% or more of the oil,” Mr Pierce explained. “And in some areas, like the Norwegian sector, even water-based cuttings cannot be disposed of overboard,” he noted. “Most cold water areas and the Mediterranean Sea follow these regulations.”

In shallow waters, anything less than 500 ft, zero-discharge regulations generally apply for both water- and oil-based cuttings. “Studies have shown that the cuttings build-up can damage the fauna and reefs in these areas,” Mr Pierce noted.

Most in the industry agree that environmental regulations will only become more stringent. “I think with the growing emphasis on reducing the environmental footprint, regulations worldwide will tighten up,” Mr Crosby said. “There will be more limits on the types of fluid that can be discharged, forcing companies to change the chemical compositions in their fluids. There also will be more procedures and policies for operators to consider.”